The impact of the Mid-Pleistocene Transition on the composition of submerged reefs of the Maui Nui Complex, Hawaii (dataset)

Brief description

The submarine reef terraces (L1–L12) of the Maui Nui Complex (MNC—the islands of Lanai, Molokai, Maui and Kahoolawe) in Hawaii provide a unique opportunity to investigate the impact of climate and sea level change on coral reef growth by examining changes in reef development through the Mid-Pleistocene Transition (900–800 ka).

Full description

Location and geological setting The MNC (Fig. 1) is toward the south-eastern end of the Hawaiian/Emperor Seamount Chain, immediately to the north-west of the Hawaiian hotspot. Shield building volcanic rock from the islands of the Complex; Molokai, Lanai, Maui and Kahoolawe (in age order) have been dated at 1.90–0.75 Ma (Clague and Dalrymple, 1989), indicating that the MNC formed since the Early to Late Pleistocene. Campbell (1986) identified six terraces off Lanai from 125 m down to 1200 m using bathymetric charts, and correlated these with submerged terraces off Hawaii based on their similar depths. [Faichney et al., 2009] and [Webster et al., 2010] identified six further terraces and labelled these submerged reefs off Lanai as L1–L12 (shallowest to deepest). Webster et al. (2010) used 87Sr/86Sr isotopes to place corals, algal laminae and echinoid spines from the deeper reef terraces around Lanai at about 1.06 Ma and 1.11 Ma for the 845 m and 925 m reefs respectively, prior to the MPT. Webster et al. (2006) dated coralline algal deposits on the tops of the two shallowest terraces at between 33.3 ka and 12.2 ka, but considered these to be thin veneers (< 5 m thick) that had grown on significantly older reef terraces. This conclusion is supported by the Webster et al. (2010) Sr dates placing L3 (305 m) at about 0.53 Ma. Taken together, these age data suggest that the stepped reef terraces in the MNC have developed since the Early Pleistocene and across the MPT. Fig. 1. (see datasets) Map of the Maui Nui Complex (MNC) showing dive locations and bathymetry. This figure is a bathymetric map of the Maui Nui Complex with a scaled down location map within the Hawaiian Islands. The mapped reef terraces are shown as solid coloured lines with dive dredge and sample location marked. Dive and dredge operations Dive and dredge sampling in the MNC has been concentrated in the south-central region (Fig. 1) thus this region comprises our study area. In 2001 the Monterey Bay Aquarium Research Institute conducted a series of dives using the ROV Tiburon. The dives included in this study are: T309, T294 and T295 south-west of Lanai at 580 m, 550 m and 475 m respectively; T310 directly south of Lanai at 150 m; and T311 and T312 north-west of Kahoolawe at 230 m and 275 m respectively. Over 139 carbonate samples were obtained from the slopes and the tops of the submarine terraces, along with about 15 h of video. Additionally, the Hawaiian Undersea Research Laboratory at the University of Hawaii has conducted Pisces submersible dives from the R/V Kaimikai-o-Kanaloa across the Complex. Samples and video from Pisces dives (P4-026, P4-027, P5-191, P5-217, P5-218 and P5-254) and video from ROV dives (RCV-108, RCV-109, RCV-110, RCV-111, RCV-115, RCV-116, RCV-117 and RCV-118) have also been used in this study. Rock dredging operations by Scripps Institution of Oceanography (91-WA and AMAT05RR-D5) and the United States Geological Survey (F2-88-HW-D32) yielded additional samples. A total of 234 limestone samples collected from these dives and dredges have been used in this study.

Sedimentology and sample analysis Limestone samples were examined in hand sample and thin section, with specific focus on the taxonomic identification of corals, coralline algae and large benthic foraminifera. The spatial context of dive samples was established from the video observations (i.e. precise sample location and whether broken off or loose). Each sample was then examined for evidence of orientation in both hand sample (e.g. discolouration and excessive growth on one side) and thin section (e.g. geopetals, growth direction, sorting, etc.). Thin section analysis was used to identify common assemblages of component grains and fossils that were then used to define sedimentary facies. These facies were compared with the modern environmental conditions of component biota to interpret their palaeoenvironments (e.g. [Adey et al., 1982], [Cabioch et al., 1999], [Fletcher et al., 2008], [Grigg, 1981], [Grigg et al., 1981], [Hallock, 1984], [Maragos, 1977], [Murray, 1991], [Renema, 2006], [Verheij, 1993] and [Veron, 2000]). The stratigraphic relationships of the facies within each sample were also recorded using cross-cutting and superposition principles to determine the sequence of palaeoenvironmental changes. Statistical analysis of facies composition Statistical analysis of the most common but compositionally diverse limestone facies was carried out. Microscope point counting of individual grains was used to examine variation in its components with respect to both depth and sample location on different terraces. This count used a Prior Model G point counter on 1 mm rows at 50 μm steps (selected from average grain size) and a 300 point sample size (for feasibility and uniformity). Forty-eight samples were selected and grains were categorised in 20 classes and prepared in matrices of sample number versus classification population. This data was analysed using Dissimilarity Matrices and Principle Components Analysis (Jongman et al., 1995) in the statistical software packages SPSS 14.0 and PcOrd. Multivariate differences between populations were tested using Multi-Response Permutation Procedure (MRPP), which is analogous to a non-parametric Manova (Zimmerman et al., 1985). To minimise the chance of a Type I error, a Bonferroni Correction was applied to the data to produce a significance level of 0.0083.

Notes

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